Permeable membranes capable of selectivity permeating a component are well known in the art and are considered advantageous means of separation in certain fluid separation applications with hollow fiber membrane geometry frequently considered the most advantageous arrangement. The construction and use of helically wound hollow fiber permeable membrane cartridges and modules incorporating said cartridges is well known in the art, also known are those cartridges wherein the hollow fibers are present in a parallel configuration, both crimped and not crimped, rather than a helical configuration, as evidenced by the prior art discussed below. The products and process of this invention are concerned with helically wound hollow fibers permeable membrane cartridges.
In practice, hollow fiber permeable membrane cartridges are constructed with both bore side feed or shell side feed configurations. This invention is concerned solely with use of bore side feed permeators in which the feed mixture is initially contacted with the inside surface or interior bore of the hollow fiber with the permeate stream recovered from the outside surface of the hollow fiber and the raffinate stream recovered from the opposite ends of the bores of the hollow fibers under the specific conditions hereinafter defined. Furthermore, this invention is concerned primarily with gas separation applications in which at least one more permeable component is separated from a mixture of gases by a permeation process through a hollow fiber membrane.
The importance of accomplishing optimal flow dynamic conditions in membrane separation applications is well recognized in the field and consequently the importance of design and construction aspects of hollow fiber permeators to accomplish these optimal flow dynamic conditions are of significant consideration. For example, in "Analysis of Gas Separation by Permeation in Hollow Fibers", C. R. Antonson et al., Ind. Eng. Chem., Proc. Des. Dev., 16, No. 4, 463-469 (1977), the use of hollow fibers for gas separation by permeation was studied in considerable detail. The entire study appears to have been made with hollow fibers in parallel arrangement, there being no indication of the use of helically wound units in the article. Among the conditions studied was the effect of flow pattern, with six flow patterns considered. FIG. 6 and the discussion on pages 466 and 467 report their findings on this aspect of their study. In general, the authors found bore feed flow patterns better than shell feed flow patterns, with bore feed, countercurrent-flow having the highest enrichment ratio and the highest fast gas recovery. The article indicates that to accomplish optimal separation conditions no gas mixing should take place in the axial direction on both the feed and permeate sides of the membrane.
U.S. Pat. No. 3,442,002, issued on May 6, 1969 to J. E. Geary, Jr., et al., discloses a fluid separation apparatus that employs bundles of hollow filaments with the fibers in each bundle in substantially parallel alignment. The patent discloses both introducing the initial mixture through the interior of the hollow filaments and introducing it to the outside of the hollow filaments, but the patent is concerned primarily with liquid separations and does not address the optimal countercurrent gas separation conditions.
Otstot et al., in U.S. Pat. No. 4,380,460 issued on Apr. 19, 1983, relates to a permeator cell in which the hollow fibers are in parallel alignment extending the length of the shell of the encasing vessel. The patent is primarily concerned with the use of a slit tube to protect the hollow fibers while being inserted into the shell. Nowhere is there any mention of helical winding, or of the importance of controlling radial mixing and axial mixing of the permeate and raffinate streams.
In U.S. Pat. No. 4,430,219, issued to Kuzumoto et al. on Feb. 7, 1984, bundles of hollow fibers are helically wound in nearly parallel relation to one another and the unit is then used in fluid separation processes. However, no attempt is made to maintain an essentially uniform hollow fiber length throughout the unit; the patent does not describe or recognize the applicability of helically wound arrangement in countercurrent gas separation applications. Further, nowhere in this published patent is there any recognition of the importance of essentially complete radial mixing of the permeate stream on the permeate side and essentially no axial mixing on either the permeate side or raffinate side of the wound permeation unit.
In U.S. Pat. No. 4,623,460, issued to Kuzumoto et al., on Nov. 18, 1986, a fluid separation unit is disclosed wherein the hollow fibers are in parallel alignment; a bundle of hollow fibers is formed in U-letter shape, potted at both ends and encased in a shell. The reference does not use a helically wound unit even though the hollow fibers may have essentially uniform length. In addition, the patentees introduce the fluid to be treated to the exterior surface of the hollow fibers not through the bores.
In U.S. Pat. No. 3,422,008, issued on Jan. 14, 1969 to E. A. McLain, permeator cartridges, generally for liquid separations, are produced by spiral winding hollow fibers around a mandrel using a pitch of at least 10.degree. and preferably 30.degree.. No attempt is made to produce a cell with essentially all of the hollow fibers having an essentially uniform length. The patent is primarily concerned with liquid separation applications and does not disclose introducing the feed through the bores or interior of the hollow fibers and also discloses shell side feed on the shell side or exterior of the fibers. The patentee also states it is generally preferable to have shell side feed to the outside of the hollow fiber and recover the permeate from the bores or the inside of the hollow fiber (column 13, lines 14 to 19). There is no disclosure of a gas separation process with countercurrent flow configuration and there is no recognition of the importance of control of radial mixing and axial mixing in such a process.
The mass transfer device used in the processes disclosed in U.S. Pat. No. 3,794,468, issued on Feb. 26, 1974 to R. J. Leonard, is of helical construction. However, in the process a first fluid is passed through the interior of the bores of the hollow fibers and a second fluid is passed around the exterior surface of the hollow fibers. A mass transfer occurs between the two fluids, as in the processes for oxygenating blood or in kidney dialysis. The process described does not necessarily provide for essentially uniform hollow fiber length or contain any recognition of gas separation applications with countercurrent flow conditions and the importance of control of radial mixing and axial mixing in permeation separation processes.
U.S. Pat. No. 4,631,128, issued to Coplan et al. on Dec. 23, 1986, discloses one of the methods for producing permeator cells in which the hollow fibers have essentially uniform length. However, this reference nowhere suggests or discloses that unexpected and unpredictable results can be achieved under the specifically described conditions of this instant invention. The Coplan et al. patent does not suggest, disclose, or recognize the importance of bore side feed while maintaining essentially complete radial mixing and essentially no axial mixing on either the permeate side or the feed side.
U.S. Pat. No. 4,734,106, issued to A. Golan, and U.K. patent applications, publication Nos. 2,122,103A and 2,022,457A, describe countercurrent gas separation with hollow fiber modules wherein hollow fibers employed are asymmetric or composite with separation layers being on the outside of the hollow fiber and with the feed gas being introduced through the hollow fiber bores with the feed permeate flown tangentially along the fiber with hollow fiber, arranged in cylindrical bundle of parallel contiguous hollow fibers. Nowhere is there any mention of the possibility of using helical winding for module construction in these publications and the surprising aspect of countercurrent flow conditions accomplished under permeate flow conditions different than tangential flow with respect to membrane surface.
None of the references recognize, suggest or disclose the importance of using a helically wound hollow fiber permeable membrane cartridge in which essentially all of the hollow fibers are of uniform length in a process for separating a fast gas stream or a component stream at enhanced permeation rate that entails bore side feeding the gas containing mixture at a positive pressure into the interior at the inlet end of the bores of the hollow fibers, removing a fast gas permeate stream from the exterior surface or shell side of the hollow fibers in a permeate flow direction that is in countercurrent flow to the feed flow direction, removing a raffinate stream at the opposite exit end of the bores of the hollow fibers in a raffinate flow direction that is in cocurrent flow to the feed flow direction while simultaneously maintaining essentially complete radial mixing of the permeate stream on the permeate side and essentially no axial mixing of either the permeate side or the raffinate side.